1. Field of the Invention
The present invention relates to an electromotive injection molding machine and a power supplying method of controlling a power supplying apparatus of the electromotive injection molding machine to supply power to servo motors that is mounted to a screw, a mold opening/shutting device, a molded product ejecting device, and the like, of the injection molding machine.
2. Description of the Related Art
An injection molding machine includes a pair of molds, a mold clamping device that mold-clamps the molds, an injection device that melts and injects resin into the molds, and the like. The injection device includes an injection cylinder, a screw that is driven in a rotating direction and an axial direction in the injection cylinder, a plunger and the like. In an electromotive type injection molding machine, the mold clamping device, the screw and the like are driven by servo motors that are independently mounted, respectively. During a molding cycle in the injection molding machine, an injection process requires higher power, even though a process time for the injection process is short, compared to the other processes. Accordingly, a large-scaled and high power servo motor is adopted for the servo motor that drives the screw in the axial direction in the injection process, so-called servo motor for an injection axis. In recent years, an ultra high-speed injection molding is highly needed which has excellent transcription and thus can mold a product having a complicated and fine shape or thin product with good transcription. In the injection molding machine capable of implementing the ultra high-speed injection molding, the injection process requires the further higher power, so that a servo motor having a larger size is adopted.
In the injection molding machine, a converter is mounted in which three-phase alternating-current (AC) voltage, which is supplied from a power receiving equipment of a factory, is converted into direct-current (DC) voltage, i.e., is rectified. The rectified DC voltage is supplied to an inverter circuit, which is equipped in relation with each servo motor, i.e., to a servo amplifier through a DC circuit. Accordingly, when the DC voltage is converted into a three-phase AC voltage of predetermined current with a predetermined frequency in the servo amplifier, the servo motor can be driven. When the servo motor for an injection axis is driven with high power, the servo amplifier is required to supply the high power to the servo motor. Hence, the high current is required with respect to current of the DC voltage to be supplied to the servo amplifier. Thus, the three-phase AC power source supplied from the power receiving equipment of a factory also requires the high current supply capability, considering the injection process in which the high output driving is required, so that the relatively high power capacity is required. Since the electric power rate structure is different depending on the contracted maximum power, the electricity rate is increased when the power receiving equipment having the high power capacity is equipped. Accordingly, a technology is needed which can reduce the power capacity required for the power receiving equipment, considering the necessities of energy saving and cost reduction, and thus decreasing the consumed electricity rate.
In JP-A-2009-241287, the inventor suggested a power supplying apparatus of an electromotive injection molding machine that stores power in a process of respective processes of a molding cycle, in which power is less consumed, supplies the stored power in a process that requires high power such as injection process, smoothes the powers required in the respective processes of the molding cycle and can reduce the maximum power to be supplied from the outside. The power supplying apparatus of JP-A-2009-241287 includes an alternating-current/direct-current (AC/DC) converter and a power storage device. The AC/DC converter is configured by a diode rectification circuit, a PWM converter, and the like. An input side of the AC/DC converter is connected to a three-phase AC power source, and an output side thereof is connected to a DC voltage line, i.e., DC circuit. The AC/DC converter rectifies the three-phase AC voltage supplied from the power receiving equipment of a factory into the DC voltage and supplies the DC voltage to the servo amplifiers provided to the respective servo motors. The power storage device is provided with a predetermined power storage circuit and is connected to the DC circuit of the output side of the AC/DC converter. By appropriately controlling the power storage circuit, it is possible to receive the power supplied from the DC circuit, to store the received power in the circuit, and to supply the stored power to the DC circuit, as required. Accordingly, by storing the power in the power storage circuit in the process of the respective processes of the molding cycle, in which power is less consumed, and by supplying the stored power in the process that requires the high output, it is possible to smooth the powers required in the respective processes of the molding cycle, so that it is possible to reduce the maximum power to be supplied from the outside. Therefore, the power capacity required for the power receiving equipment of the factory is also decreased, so that it is possible to reduce not only the equipment cost but also the required electricity rate.
The power supplying apparatus disclosed in JP-A-2009-241287 can store the power and supply the stored power, as required. Therefore, it is possible to smooth the power required in the respective processes of the molding cycle in the injection molding machine and to reduce the maximum power to be supplied from the three-phase AC power source. However, the power supplying apparatus disclosed in JP-A-2009-241287 seems to have problems to be solved. That is, JP-A-2009-241287 does not disclose a method of optimally controlling the power supplying apparatus. More specifically, JP-A-2009-241287 discloses a method of solely controlling the power storage circuit itself and a method of storing or supplying the power. However, JP-A-2009-241287 does not disclose a method of controlling the power storage circuit in conjunction with the control on the DC/AC converter or servo amplifiers. The power storage circuit, the DC/AC converter and the servo amplifier are connected to each other by the DC circuit. Accordingly, if they are independently controlled each other, a change in the DC voltage due to the other control causes disturbance, so that it becomes difficult to perform the appropriate control. In addition, even when the power storage circuit, the DC/AC converter and the servo amplifier are controlled in conjunction with each other, a specific control method thereof is unclear. Hence, there is no guarantee that can securely cope with the high power, which is instantaneously required when performing the injection process, for example. That is, there is no guarantee that can sufficiently reduce the maximum power.